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Scientific and Natural Areas Program

Minnesota Scientific and Natural AreasPatterned Peatlands

The vast peatlands of northern Minnesota are some of the most intriguing landscapes in the world and one of the state's most extensive ecosystems. They cover more than 10% of the state.

Unlike Minnesota's other large ecosystems such as prairies and broadleaf forests, most of Minnesota's peatlands have not been cleared or fragmented by development. The expansive, mostly unaltered patterned peatlands of the Lake Agassiz Lowlands are recognized internationally for their significance. They present a rare opportunity in Minnesota for landscape-scale conservation and research on peatland development.

Extensive glacial lake plains lie within the Laurentian Mixed Forest Province of Minnesota providing an ideal setting for the development of peatlands. An intricate relationship between vegetation, subtle topography, hydrology and climate has formed some of the largest and best developed peatlands in North America.

Formation

Minnesota's peatlands began to form 5-6,000 years ago when the climate cooled and precipitation increased significantly. This change in climate helped facilitate the formation of the large peatlands we see today. Peat formation exists on all continents and at all latitudes, including tropical marshes and swamps. Variations in climate, hydrology, native species, and other factors result in the considerable variety of peatland communities found around the world. Peatlands in Minnesota and latitudes farther north in Canada, Europe, and Siberia are characterized as boreal peatlands.

Peat formation requires low-oxygen conditions that prevent normal decomposition of plant debris. This occurs in areas of poor drainage where precipitation exceeds evaporation. The water table lies at or near the surface in these areas, saturating dead plant material. As a result, organic materials accumulate year-after-year, forming the partially decomposed mass known as peat.

A useful source of information on these fascinating ecosystems can be found in the book, The Patterned Peatlands of Minnesota. The book was edited by H.E. Wright, Jr., Barbara Coffin, and Norman E. Aaseng, and published by the University of Minnesota Press in 1992. Most of the information in the following discussion comes from this source.

Significance

At over 6 million acres, Minnesota has more peatlands than any other state in the U.S. except Alaska. The large, mostly unaltered peatlands of northern Minnesota are recognized regionally and internationally for their expansiveness and spectacularly patterned landscape. They provide excellent opportunities to study and understand intricate hydrological patterns that can develop over large peatland areas with diverse water chemistry, flow patterns, and ecological processes. They are also important for research on how peatlands affect the world's climate.

Minnesota's northern peatlands are more accessible to researchers relative to other large boreal peatlands in places such as Siberia and Canada's Hudson Bay lowlands. They are also relatively free of development, unlike accessible peatlands in northern Europe, which have been altered by commercial use. Minnesota's large peatlands are also among the few patterned peatlands in the world not underlain by permafrost. Permafrost makes it difficult to investigate groundwater hydrology and the subtle drainage systems essential to peatland formation and development.

By accumulating dead organic matter as peat, peatlands play a significant role in carbon sequestration and the global carbon cycle, and scientists are extremely interested in understanding any effects of climate change on the world's peatlands. Minnesota's large peatlands are unusual in North America in their proximity to the prairie-forest border. The highly developed and patterned Red Lake Peatland in north central Minnesota is, in fact, within 50 miles of the prairie border. At this boundary, evapotranspiration begins to exceed precipitation and conditions become unfavorable for peatland development. As a result, these peatlands are considered especially vulnerable to fluctuations in climate and may provide scientists with early indication of the effects of climate change on North America's peatlands.

In recognition of their significance, the legislature enacted the Wetland Conservation Act of 1991 (WCA), which established 18 peatland Scientific and Natural Areas.

Bogs and Fens

Peatland vegetation reflects the relationships among plants, topography, climate, and water, which are very different from those found on other Minnesota landscapes. Boreal peatland plant communities can be divided into two groups, bogs and fens.

Bogs develop where peat builds up over time and the peat surface becomes elevated, isolating it from mineral-rich runoff or groundwater. In these settings, all nutrient inputs come solely from precipitation and wind-blown dust. Surface water in these systems is very acidic (pH <4.2). Fewer plants and animals have adapted to these conditions than in fens and other wetland communities. Sphagnum mosses, ericaceous shrubs (plants in the heath family such as leather leaf), and sedges dominate the ground layer. Bogs may either be forested, with sparse to patchy canopies of stunted (less than 30 feet tall) black spruce and occasional tamarack trees; or open, with trees either absent or scattered and short.

Fens have groundwater that has percolated through mineral soil, flowing continuously at or near the surface and in contact with plant roots. Surface water pH is moderately acidic to neutral, ranging from 5.6 to 7.0. Fens appear like saturated meadows, with abundant sedges, rushes, and other grass-like plants, as well as occasional shrubs, and scattered stunted trees, such as tamarack.

Water flow and sources in bogs and fens

Peatland Landforms

The amount of moving water varies throughout peatlands, and complex patterns can develop in response to subtle gradients in water flow and chemistry. These patterned peatlands are composed of complexes of bogs and/or fens. Three landforms are common in Minnesota's northern peatlands: raised bogs, water tracks, and spring fens. They can occur individually within a peatland or together in complexes of various combinations and stages of development.

Raised bogs are one of Minnesota's most prominent peat landforms. These forested areas are domed in cross section, isolating the bog surface from mineral-rich runoff draining from adjacent uplands. When a bog has developed sufficiently in elevation, it forms a crest of black spruce that radiates out from the center, when viewed from aerial photos. Trees gradually become more stunted downslope from the crest as the peat becomes more saturated. At the lower margins, spruce trees give way to non-forested sphagnum lawns (muskeg). Raised bogs can also occur as circular or, egg-shaped ovoid islands that lack crests of black spruce. Circular or ovoid islands generally form when adjacent to water tracks (see below).

Water tracks are fen areas in peatlands that look like river channels on aerial photos. They are concave in cross section and oriented downslope in the direction of water flow. Water flow is imperceptible on the ground because of the very subtle change in topography (1 foot in elevation for every 1,000 to 2,000 feet of distance). Water tracks are often bordered by swamp forests or raised bogs. A water track may be patterned or featureless:

Patterned water tracks or fens contain networks of peat ridges (known as ribs or strings) and pools (known as flarks) that form perpendicularly to the slope and flow of water. These patterns resemble ripples when viewed from aerial photos. These water tracks may also contain teardrop-shaped tree islands, that are oriented parallel to the prevailing slope and flow of water.

Featureless water tracks lack the ripple patterns of patterned water tracks, although they may have linear bands of tree islands parallel to the flow of water.

Spring fens develop where groundwater wells up strongly, through the peat layer. The flow of discharging groundwater forms a network of narrow channels that flow through and dissect black spruce and tamarack swamp forest. The channels often rejoin as they flow, creating small linear-shaped swamp forest islands. The water in spring fens is cold, oxygen poor, and highly calcareous (alkaline), reflecting the ground water source.

The table below shows the kinds of landforms in each of Minnesota's 18 peatland SNAs.

Peatland Plants

Despite the harsh conditions of peatland environments, a variety of plants are well adapted to these wetland types. Most plants are evergreen to retain scarce nutrients, in contrast with deciduous plants, which lose nutrients when leaves are shed. Many plants, such as the ericaceous shrubs leather leaf and Labrador tea, have thick leathery leaves and alkaloids in leaf tissue to reduce browsing. Most peatland plants are adapted to survive with very low nutrient concentrations. A few characteristic peatland species, such as pitcher plant, sundews, and bladderworts, have developed ways of capturing and digesting insects to supplement nutrients.

Sedges, cotton grasses, and a nearly continuous mat of sphagnum moss species

Sedges, brown mosses (sphagnum moss species are not abundant if present), and aquatic species

Peatland Animals

Peatlands provide relatively sparse cover and food for large animals, so few large mammals are associated with peatlands. Woodland caribou did thrive in Minnesota's large peatlands until their migration routes to Canadian breeding grounds were cut off in the 1900s. The small bands that were stranded in Minnesota peatlands died off. Moose and timber wolves inhabit the edges of the peatlands, where forest cover and browse species are available. Construction of ditches during early statehood has allowed beaver and muskrat to increase in numbers in peatlands, along with predators, otter and mink.

As with large mammals, few small mammals species inhabit peatlands. Many mammals require dry nest sites, shelter, upland food sources, or sites for burrowing, which peatlands do not provide. Bog lemmings are one of the few small mammals specifically adapted to peatland habitats. Some species of shrews and voles also inhabit peatlands. Although animals of the peatlands may be difficult to observe directly, watchful visitors can find evidence of their activity, such as sedge "haystacks" piled in the sun (bog lemmings), heaps of spruce cone bracts (red squirrel), or pruned alder stems (snowshoe hare).

Migratory bird species bring interest to the peatlands in spring and summer breeding months. Their preferences for food and cover draw them to bog or fen habitats, as shown in table below. Great gray owls are permanent residents of northern Minnesota's peatlands, nesting in forested peatlands. No federal or state endangered or threatened bird species occur in Minnesota's peatlands, although 14 state special concern species use open fen or peatland forest habitat.

Amphibians and reptiles that inhabit peatlands are relatively limited. More frogs and toads are adapted to this environment than turtles, lizards, and snakes. Species' requirements for moisture, pH levels, temperature, and nutrition govern distribution. For example, terrestrial burrowers and aquatic species that require deep water that does not freeze to the bottom are generally absent. Species that need to breed early in spring to reproduce successfully are limited by the short summer season. Acidity of bog water affects the survival of creatures using it as a breeding medium.

Insects inhabit the peatlands in abundance, though there remains much to be learned about them. Visitors will find ample mosquitoes, damselflies, dragonflies, and deerflies.